1. Field of the Invention:
The present invention relates to a developer carrier for use in a dry-type image developing device which employs a one-component developer in an electrophotographic copier or an electrostatic recording apparatus.
2. Description of the Prior Art:
There is known a developer carrier such as a developing roller having an electrically insulative resin layer around the peripheral surface thereof, the developer carrier being used as a means for bringing a one-component developer into contact with an electrostatic latent image on an electrostatic latent image carrier such as a photosensitive drum to develop the electrostatic latent image into a visible image. In order to remove an electric residual image from the developer layer on the developer carrier after the image development, the resin layer on the developer carrier must be made of a material exhibiting strong polarity such as urethane, epoxy, or the like which is of relatively high electric conductivity. The electric conductivity of these materials greatly varies as ambient conditions such as temperature and humidity vary, failing to provide stable image developing characteristics.
There is also known a developer carrier having a resin layer made of highly insulative acrylic resin, for example, the resin layer having a plurality of electrodes scattered as islands therein, each of the electrodes being of a size larger than the diameter of a developer particle. With this type of developer carrier, if an inverse bias voltage applied to a lightly charged developer is high, charges are moved from the electrodes to the developer for thereby producing a developer charged in opposite polarity, with the result that the amount of the developer consumed is increased.
It has been found that the image developing characteristics vary due to changes in the electric resistance of the resin layer on the developer carrier which are caused by absorption of moisture into the resin and dispersion of moisture from the resin.